A visitor of the values of annotation type elements, using a
variant of the visitor design pattern. Unlike a standard visitor
which dispatches based on the concrete type of a member of a type
hierarchy, this visitor dispatches based on the type of data
stored; there are no distinct subclasses for storing, for example,
boolean values versus int values. Classes
implementing this interface are used to operate on a value when the
type of that value is unknown at compile time. When a visitor is
passed to a value's accept method,
the visitXYZ method applicable to that value is
invoked.

Classes implementing this interface may or may not throw a
NullPointerException if the additional parameter p
is null; see documentation of the implementing class for
details.

WARNING: It is possible that methods will be added to
this interface to accommodate new, currently unknown, language
structures added to future versions of the Java™ programming
language. Therefore, visitor classes directly implementing this
interface may be source incompatible with future versions of the
platform. To avoid this source incompatibility, visitor
implementations are encouraged to instead extend the appropriate
abstract visitor class that implements this interface. However, an
API should generally use this visitor interface as the type for
parameters, return type, etc. rather than one of the abstract
classes.